#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <chrono>
#include <cmath>
#include <cstdint>
#include <cstring>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <vector>
#include <climits> 
using namespace std; 
#define endl '\n'
#define all(x) begin(x), end(x)
 
void dbg_print(int x) {cerr << x;}
void dbg_print(long x) {cerr << x;}
void dbg_print(long long x) {cerr << x;}
void dbg_print(unsigned x) {cerr << x;}
void dbg_print(unsigned long x) {cerr << x;}
void dbg_print(unsigned long long x) {cerr << x;}
void dbg_print(float x) {cerr << x;}
void dbg_print(double x) {cerr << x;}
void dbg_print(long double x) {cerr << x;}
void dbg_print(char x) {cerr << '\'' << x << '\'';}
void dbg_print(const char *x) {cerr << '\"' << x << '\"';}
void dbg_print(const string &x) {cerr << '\"' << x << '\"';}
void dbg_print(bool x) {cerr << (x ? "true" : "false");}
template<typename T, typename V>
void dbg_print(const pair<T, V> &x) {cerr << '{'; dbg_print(x.first); cerr << ','; dbg_print(x.second); cerr << '}';}
template<typename T>
void dbg_print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? "," : ""), dbg_print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {dbg_print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
template<size_t T>
void dbg_print(bitset<T> b) {cerr << b;}
#ifndef ONLINE_JUDGE
#define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
#define debug(x...)
#endif
 
// ============================================================================================== // 

typedef long long ll; 

struct base {
    double a, b;
    base(double _a = 0, double _b = 0) : a(_a), b(_b) { }
    const base operator+(const base &c) const { return base(a + c.a, b + c.b); }
    const base operator-(const base &c) const { return base(a - c.a, b - c.b); }
    const base operator*(const base &c) const {
        return base(a * c.a - b * c.b, a * c.b + b * c.a);
    }
};

const double PI = acos(-1);

void fft(vector<base> &a, bool inv = 0) {
    int n = (int)a.size();

    for (int i = 0; i < n; i++) {
        int bit = n >> 1, j = 0, k = i;
        while (bit > 0) {
            if (k & 1) j += bit;
            k >>= 1, bit >>= 1;
        }
        if (i < j) swap(a[i], a[j]);
    }

    double angle = 2 * PI / n * (inv ? -1 : 1);
    vector<base> wn(n / 2);
    for (int i = 0; i < n / 2; i++) wn[i] = {cos(angle * i), sin(angle * i)};

    for (int len = 2; len <= n; len <<= 1) {
        int aux = len / 2;
        int step = n / len;
        for (int i = 0; i < n; i += len) {
            for (int j = 0; j < aux; j++) {
                base v = a[i + j + aux] * wn[step * j];
                a[i + j + aux] = a[i + j] - v;
                a[i + j] = a[i + j] + v;
            }
        }
    }

    for (int i = 0; inv && i < n; i++) a[i].a /= n, a[i].b /= n;
}

vector<int> multiply(vector<int> &ta, vector<int> &tb) {
    int n = (int)ta.size(), m = (int)tb.size();
    int t = n + m - 1, sz = 1;
    while (sz < t) sz <<= 1;

    vector<base> a(sz), b(sz), c(sz);

    for (int i = 0; i < sz; i++) {
        a[i] = i < n ? base((double)ta[i]) : base(0);
        b[i] = i < m ? base((double)tb[i]) : base(0);
    }

    fft(a, 0), fft(b, 0);
    for (int i = 0; i < sz; i++) c[i] = a[i] * b[i];
    fft(c, 1);

    vector<int> res(sz);
    for (int i = 0; i < sz; i++) res[i] = int(round(c[i].a));

    while ((int)res.size() > t && res.back() == 0) res.pop_back();

    return res;
}

const int maxn = 1e6 + 1000; 
int spf[2*maxn]; 
vector<int> primes; 

int main() {
    ios_base::sync_with_stdio(0); 
    cin.tie(0); 

    for (int i = 2; i < 2*maxn; i++) {
        if (spf[i] == 0) {
            primes.emplace_back(i); 
            spf[i] = i; 
        } 
        for (int p : primes) {
            if (i * p >= 2*maxn || p > i) break; 
            spf[i * p] = p; 
        } 
    } 

    int n; cin >> n;
    vector<int> freq_even(maxn / 2 + 1), freq_odd(maxn / 2 + 1); 
    int cnt_1 = 0; 
    for (int i = 0; i < n; i++) {
        int c; cin >> c; 
        cnt_1 += c == 1; 
        if (c&1) freq_odd[c / 2] = 1; 
        else freq_even[(c - 1) / 2] = 1; 
    } 

    if (cnt_1 <= 1) cout << 2 << endl;
    else {
        auto ret = multiply(freq_even, freq_odd); 
        for (int i = 0; i < ret.size(); i++) {
            if (ret[i] == 0 && spf[2*(i + 1) + 1] == 2*(i + 1) + 1) {
                cout << 2*(i + 1) + 1 << endl;
                break; 
            } 
        } 
    } 
}